WUI Access via LDAP, old local Users can't login



we wanted to change our WUI login to LDAP authentication. We're using the KEMP LB for some time now and used to use local users, but now want to use LDAP.

We configured a LDAP endpoint, a Remote Group and the WUI Authentication with the setting Domain set to our domain name. This works for new users, that had no local user on the LB. They can connect with only there usernam, they don't need to add the "@domainname" for login (also when we use the "Test AAA for User" it works).

But for the old users, that had a local user, it doesn't work. Even after deleting the local user account , they have to use "username@domainname" for login.

Our "old" local usernames were the same usernames as in our LDAP (MS AD) directory.

Example: my local user was admin1 and in our AD my users samaccountname is admin1.

Is the local user saved somewhere, even after deleting them? Do they have to be purged somehow. Even a reboot of the appliance (it's a HA cluster, I only rebooted the active one) it doesn't work.